Papers by Author: S.O. Osuji

Abstract: Two coarse-grained granitic rocks - charnockite and biotite granite were studied with the aim of estimating their unconfined compressive strength from simpler non-destructive test values. The simpler tests were the ultrasonic pulse velocity, the Schmidt hammer rebound, and the specific gravity. Another test carried out was the moisture absorption. The rocks had compressive strength in the range 115-250 MPa, Schmidt hammer rebound number or index of 35-55, and pulse velocity of 3.4-5.5 km/s. The correlation coefficients between the uniaxial compressive strength and the rebound number were 0.86 and 0.81 for the biotite granite and the charnockite, respectively. Products of the rebound index and the pulse velocity and the specific gravity improved the correlation coefficients to 0.94 and 0.91 respectively. The high correlation factors implied that the compressive strength can be estimated using the simpler tests parameters. These simpler parameters also relate indirectly to geomechanical properties of the rocks such as drillability, boreability and machine tool wear. The moisture absorption alone and its combination with the rebound number correlated inversely and poorly with the compressive strength. The correlation coefficient ranged between 0.45 to 0.67. The moisture absorption therefore proved to be a poor predictor of the uniaxial compressive strength of the rocks.

Abstract: The behaviour of the core of rockfill dam with slanting clay core was investigated with the Jebba main dam, Nigeria as a case study. The stress-deformation behavior of the dam was studied using the finite element mathematical modeling technique. The actual fill properties were utilized and two loading scenarios-no water and full reservoir operations-were investigated. At full reservoir, the actual seepage line, as recorded over the years was used. The linear total stress analysis using the finite element method of analysis was employed to analyze the dam section. Following the finite element mathematical modeling and computer simulations of the models, deformations and stresses distributions were determined. The results showed that the observed longitudinal cracks at the Jebba main dam crest are as a result of potential cracks in the dam core section. The cracks observed at the crest, from analysis, commenced from the dam’s core upstream face, downstream face and core crest. This may have resulted from probable hydraulic fracturing and tensile stresses developments in these regions. The results also showed likely loss of integrity of core due to cracks. However, total collapse may not be experienced but dam performance may be impaired and alarming visible cracks may not be ruled out over time.